Until recently, streaming of media files was realized using the real time streaming protocol RTSP as control protocol. The transmission of the streaming data itself is not the task of the RTSP protocol, the real time transport protocol RTP being used for media transport and the session description protocol SDP being used for session description. HTTP streaming is used for transmission of media data using a conventional web server. Media files can also be transferred without a RTSP server using progressive download. Progressive download describes a technique where the media file is progressively downloaded to the end-user and, as soon as enough data are present on the receiving side, the playout is started. HTTP streaming and progressive download using HTTP is becoming more important. By way of example, some cellular phones only support progressive data download using .mp4 or .3gp file formats.
Content download including HTTP streaming and progressive download is not defined for the IP multimedia subsystem IMS, IMS providing an architecture offering voice over IP and multimedia services. In case of HTTP traffic an interactive bearer is requested and set up by the radio access network RAN. For download of general data like web pages an interactive bearer is sufficient. However, HTTP streaming and progressive download using HTTP have other requirements than general HTTP file download. By way of example, a guaranteed bit-rate is necessary, since a continuous media delivery and playout is needed. Compared with RTP streaming, the requirements for HTTP streaming are also different, as HTTP uses TCP (transfer control protocol) with its in-built retransmission mechanisms. The retransmission mechanism retransmits a data packet lost during transmission. Thus, HTTP streaming needs a bearer with higher bit-rate and/or lower error rate compared to RTP streaming, as every lost data packet is retransmitted increasing the data to be transmitted. Thus, a low error rate is advantageously used.
Currently, there are no mechanisms that detect the need of a quality of service (QoS) bearer in case of using HTTP for streaming or progressive download, calculate the parameters of the quality of service bearer and set up the quality of service bearer, e.g. in the IMS domain. Quality of service means that a specific service, such as streaming a media file, will be quantitatively and qualitatively provided as expected by the end-user by using resource reservation control mechanisms in the network and by providing the ability to use different priorities for different applications. In present networks, if the user downloads a media file using HTTP streaming or progressive download using HTTP, it cannot be assured that the bearer has the appropriate bandwidth and error rate needed for a data transfer satisfying the end-user.